Web tensioning support

ABSTRACT

A web tensioning support for a roll of sheet material to permit the sheet material to be withdrawn from the roll by a generally uniform force. An arbor is formed to support the roll of sheet material for rotation therewith and the arbor is supported for rotation by an arbor support and brake which frictionally engages the arbor along a surface area spaced from the axis of the arbor. A constant braking torque is applied to the arbor to counterbalance the decrease in the force required to withdraw the sheet material from the roll against the frictional force applied by the arbor support and brake as the roll of sheet material is depleted.

* tates atent 1 [54] WEB TENSIONING SUPPORT [75] Inventor: John W. Ulseth, Saint Paul, Minn.

[73] Assignee: Minnesota Mining & Manufacturing Company, St. Paul, Minn.

[22] Filed: May 13, 1971 [21] Appl. No.: 142,948

[56] References Cited UNITED STATES PATENTS 3,539,127 11/1970 Growey ..242/75.43 X

2,983,463 5/1961 Aaron ..242/75.43 2,777,545 1/1957 ROckett ..242/75.4 X

[ 51 May 22, 1973 FOREIGN PATENTS OR APPLICATIONS 209,704 6/1960 Germany ..242/75.4

Primary Examiner-George F. Mautz Assistant Examiner-Edward J. McCarthy Attorney-Kinney, Alexander, Sell, Steldt & Delahunt [57] ABSTRACT A web tensioning support for a roll of sheet material to permit the sheet material to be withdrawn from the roll by a generally uniform force. An arbor is formed to support the roll of sheet material for rotation therewith and the arbor is supported for rotation by an arbor support and brake which frictionally engages the arbor along a surface area spaced from the axis of the arbor. A constant braking torque is applied to the arbor to counterbalance the decrease in the force required to withdraw the sheet material from the roll against the frictional force applied by the arbor support and brake as the roll of sheet material is depleted.

4 Claims, 3 Drawing Figures Patented May 22, 1973 INVENTOR. JOHN W ULSETH BY RAD/us 0F ROLL J M FIG 3 ATTORNEYS WEB TENSIONING SUPPORT FIELD OF THE INVENTION The present invention relates to a support for a roll of sheet material having a hollow cylindrical core to permit withdrawal of the sheet material from the roll under a generally uniform tension.

BACKGROUND OF THE INVENTION In many applications (i.e., photocopying machines) it is necessary and/or convenient to provide a sheet material in roll form and to withdraw the sheet material from the roll as it is needed. The roll of sheet material must be supported in a manner to provide a back tension in the sheet material so that the momentum of the roll will not cause the sheet material to be spilled from the roll after the drive withdrawing the material from the roll is discontinued. The back tension must, of course, be less than the force required to tear the sheet material and preferably it should remain constant as the sheet material is depleted to facilitate uniform withdrawal and feeding of the sheet material.

In many instances back tension in a web has been provided by constant braking torque applied to the spindle or arbor supporting the roll of sheet material. This method has been disadvantageous in that as the radius of the roll of sheet material decreases the force required to withdraw the sheet material from the roll increases as the reciprocal of the radius. To compensate for this increase, some of the more complex mechanisms sense the decrease in the radius of the roll and decrease the braking torque as the roll radius decreases. Other prior art mechanisms have provided the back tensioning in the web by supporting the arbor or spindle on a friction surface which supports the weight of the arbor and the roll of sheet material and permits them to rotate against the frictional force between the arbor and the friction material. With this type of mechanism as the radius of the roll decreases, the force required to withdraw the sheet material from the roll also decreases. The more complex mechanisms of this type include means to compensate for the decrease in the weight of the roll, as exemplified by U. S. Pat. No. 3,567,148 in which the roll of sheet material is supported at the end of a counterbalanced arm. Thus, to avoid a constantly increasing or constantly decreasing force required to withdraw a sheet material from a roll, the prior art has provided expensive compensating mechanisms.

SUMMARY OF THE INVENTION A web tensioning support for a roll of sheet material to permit the sheet material to be withdrawn from the roll under a generally uniform tension. A cylindrical arbor is formed to support the roll of sheet material for rotation therewith. An arbor support and brake supports the arbor for rotation by frictionally engaging the arbor along a surface area spaced from the axis of the arbor and a constant braking torque is applied to the arbor in counterbalancing relationship to the frictional force applied by the arbor support and brake. As the sheet material is withdrawn from the supported roll the constant braking torque applied to the arbor tends to increase the force necessary to withdraw the sheet material and the frictional force tends to decrease the necessary withdrawal force thereby aiding in maintaining the withdrawal force and the tension in the web constant.

THE DRAWINGS In the drawings:

FIG. 1 is an end view of a web tensioning support constructed in accordance with the present invention;

FIG. 2 is a top view of the web tensioning support of FIG. 1; and

FIG. 3 is a graphical representation of the performance of the web tensioning support of FIG. 1 in comparison to prior art devices.

Referring now to the drawings, there is illustrated a web tensioning support, generally designated 10, constructed in accordance with the present invention. The web tensioning support 10 comprises an arbor 12, an arbor support and brake l4 and means 16 for applying a constant braking torque to the arbor 12.

The arbor 12 comprises a hollow cylindrical tube formed to fit within and extend from the ends of a hollow core 18 of a roll of sheet material 19. The arbor 12 is formed with a key 13 extending radially from its periphery to fit within a keyway slot 20 in the end of the roll core 18 to couple the roll of sheet material 19 to the arbor 12 for rotation therewith.

The arbor support and brake 14 comprises a pair of support blocks 22 and 25 formed with semi-circular recesses in their upper surfaces and having a strip of friction material 26 secured to the base of their recesses. The support blocks 22 and 25 are spaced to support the ends of the arbor on the strips of friction material 26 and the friction material engages approximately of the peripheral surface of the arbor.

The means 16 for applying a constant braking torque to the arbor 12 comprises a pair of leaf springs 28 and 31, each being secured by one end to the upper surface of one of the support blocks 22 and 25, respectively. Each leaf spring is formed to extend over the arbor adjacent one end of the arbor l2 and has a strip of a friction material 32 secured adjacent its free end. The leaf springs 28 and 31 are chosen to apply a constant force between the friction material 32 and the ends of the arbor 12. The constant braking torque applied by the leaf springs 28 and 31 and their friction material 32 is chosen to counterbalance the change in web tension effected by the arbor support and brake 14 as the roll of sheet material is depleted.

An idler roller 34 is provided as a guide over which the sheet material 19 may be withdrawn from the roll by a pair of drive rollers 36 and 37.

The tension created in the sheet material during withdrawal by the arbor support and brake 14 alone is:

T, (p r/R) [W+w TcosO TsinO] wherein:

T the web tension developed by the arbor support and brake.

t, the friction factor between the arbor surface and the arbor support friction material 26.

r the exterior radius of the arbor.

R the radius of the roll of sheet material.

W the weight of the roll of sheet material.

w the weight of the arbor T (pg/RhrRLd] p rrrLdR wherein.

L the axial length of the roll of sheet material.

d the density of the sheet material. From equation (2) it can be seen that the web tension due to the arbor support and brake 14 alone linearly decreases as the radius of the roll of sheet material decreases.

The additional tension created in the sheet material by the leaf springs 28 and 31 and their friction material 32 is:

wherein:

f the force of the leaf springs bearing against the arbor.

4. the friction factor between the arbor surface and the leaf spring friction material 32. and the constant torque developed by the leaf springs and their friction material is:

3 z fll i F2] From equation (3) it can be seen that the additional web tension is inversely related to the radius of the roll of sheet material and increases non'linearly as the radius of the roll of sheet material decreases. For further simplicity the friction material 26 on the arbor supports and the friction material 32 on the leaf springs are the same materials so that #2 p., T (2p.rf/R) and t 2 ,urf. The equation for the total web tension is then:

T= T T mrLdR +(2p.rf/R) T= prrrLdR t/R The proper choice of the relationship between pmrrLd and I will produce a counterbalancing effect between T, and T so that their combination will provide greater uniformity in the necessary withdrawal force, T, than either produces alone. Choosing the radius of the arbor as 1 inch minimum radius of the roll of sheet material to avoid the effect of the rapid growth of T as R 6 approaches zero, a proper numerical relationship is achieved by:

wherein:

R the maximum radius of the roll of sheet material.

FIG. 3 is a graphical representation of the web tension as a function of the radius of the roll of sheet material utilizing the simplified formulas to illustrate the principle of operation. In constructing the graph of FIG. 3, R is set at 5 inches and tr'rrLd is arbitrarily set equal to 1 so that according to equation (7) t= 5 inches per pound. These values may be attained with a roll of sheet material having a density, d 0.04 pounds/inches and a length, L 8.5 inches if the frictional and arbor materials are chosen to have a coefficient of friction, p. 0.95 and the total spring force, f 2.6 pounds. Using equation (6), T was calculated and it is represented by the full line in FIG. 3. The web tensions T and T were then calculated and plotted so that they would pass through the same point as Tat the average radius of the roll (3 inches). T is represented in FIG. 3 by the short dashed lines and T is represented by the short and long dashed lines. The variation in T as R goes from 5 to l is approximately 1.5 pounds, the variation in T is approximately 6.4 pounds, and the variation in T is approximately 1l.3 pounds. Thus, T in this simplified model is more than four times better than either T or T alone.

While the assumptions made above in describing the principle of operation of the present invention can be physically realized they are not meant to limit the present invention. Any combination of the frictional force and the constant braking torque which produces a lesser variation in the web tension as the sheet material is withdrawn then is produced by the frictional force or the constant braking torque separately is a proper counterbalancing combination in accordance with the present invention.

Having thus described the present invention, what is claimed is:

I. A web tensioning support for a roll of sheet material, comprising:

an arbor having a cylindrical support surface spaced from its axis and formed to coaxially support the roll of sheet material for rotation therewith,

arbor support and brake means for supporting said arbor for rotation by frictionally engaging said arbor along said support surface, and

means for applying a constant braking torque to said arbor to counterbalance the decrease in the force required to withdraw the sheet material from the roll against the frictional force applied by said arbor support and brake means as the roll of sheet material is depleted,

whereby as the sheet material is withdrawn from the supported roll the frictional force applied to the arbor tends to decrease the force necessary to withdraw the sheet material and the counterbalancing constant braking torque tends to increase the necessary withdrawal force thereby aiding in maintaining the withdrawal force constant.

2. The support of claim 1 wherein said means for applying a braking torque is numerically related to said arbor support and brake means by the formula [p.r'rrLd] R t wherein:

R the radius of the full roll of sheet material;

t= the braking torque applied by said means for applying a braking torque to said arbor;

r radius of arbor at which said arbor support and brake means frictionally engages said arbor;

[.L the friction factor between said arbor and said arbor support and brake means;

L the axial length of the roll of sheet material; and

d the density of the sheet material.

3. The support of claim 1 wherein said arbor has cylindrical end portions formed to extend from the ends of a said roll of sheet material and wherein said means for applying a constant braking torque comprises a pair face of the end portion of said arbor III 

1. A web tensioning support for a roll of sheet material, comprising: an arbor having a cylindrical support surface spaced from its axis and formed to coaxially support the roll of sheet material for rotation therewith, arbor support and brake means for supporting said arbor for rotation by frictionally engaging said arbor along said support surface, and means for applying a constant braking torque to said arbor to counterbalance the decrease in the force required to withdraw the sheet material from the roll against the frictional force applied by said arbor support and brake means as the roll of sheet material is depleted, whereby as the sheet material is withdrawn from the supported roll the frictional force applied to the arbor tends to decrease the force necessary to withdraw the sheet material and the counterbalancing constant braking torque tends to increase the necessary withdrawal force thereby aiding in maintaining the withdrawal force constant.
 2. The support of claim 1 wherein said means for applying a braking torque is numerically related to said arbor support and brake means by the formula ( Mu r pi Ld) Rmax t wherein: Rmax the radius of the full roll of sheet material; t the braking torque applied by said means for applying a braking torque to said arbor; r radius of arbor at which said arbor support and brake means frictionally engages said arbor; Mu the friction factor between said arbor and said arbor support and brake means; L the axial length of the roll of sheet material; and d the density of the sheet material.
 3. The support of claim 1 wherein said arbor has cylindrical end portions formed to extend from the ends of a said roll of sheet material and wherein said means for applying a constant braking torque comprises a pair of similar resilient members extending one over each end of the supported arbor, each said resilient member carrying a friction material over said arbor into engagement with the surface of the supported arbor with a predetermined force.
 4. The support of claim 3 wherein said arbor support and brake means comprises a pair of similar support members formed and spaced to support said end portions of said arbor, each said support member including a friction material positioned to support an end portion of said arbor by engagement with the peripheral surface of the end portion of said arbor. 